Heretofore a typical patient stereotactic apparatus has involved a head ring which is attached by posts and sharpened head screws to the patient's cranium, as shown in FIG. 1. The ring 11 encircles the patient's head 12, and is secured to the head by posts such as 14 with head screws 15 at the tips of the posts that can be securely placed into the outer table of the patient's skull. Alternately, the ring may have a dental impression means to register to the patient's teeth (see Radionics GTC System), or the ring may have a mask mold of the face or head to immobilize relative to the head external contours (see the Fisher Heidelberg Mask System). The ring can accept graphic reference localizers which enable scanner index data from tomographic scanning such as CT, MR, P.E.T., etc. to be used to relate two-dimensional or three-dimensional tomographic scan data from an image scanner to the coordinate reference frame of the ring 11. Once the "stereotactic coordinates" of a selected target position seen in the image scan data are determined relative to ring 11, a stereotactic arc system can be used attached to the ring to direct a probe to the physical target corresponding to the selected target position seen from these scan image data. In another context, the ring can be attached to a couch such as 18 by means of ring holders 16, and a delivery of radiation from a LINAC through a collimator system such as 17 can be directed to the stereotactic target coordinates of the selected target position. These are examples of stereotaxy using a patient immobilizer and graphic reference means from the prior art, and are illustrated by the apparatus such as the BRW Stereotactic System of Radionics, Inc.
The use of skull-attached head rings or dental impression or mask impression-attached head rings has limited usefulness for irradiation of the head region. Specifically, the ring is an obstruction to probe and also to radiation beams, for which it may be desirable to aim at targets at the very lowest part of the skull, the nasal pharynx, jaw, neck, and upper thorax. In this situation, a ring structure placed around the head, as shown in FIG. 1, is obstructive and an impediment to desired beam entry directions. The ring can be placed high on the patient's head, but this too may limit the solid angle of access of the beams to the skull base and nasopharynx. The head ring also may prevent wide angulation of the head relative to the couch in some cases.
The patent of Abele and Koslow, U.K. Patent 2,094,590 shows a mouth bite piece type head stabilizer with upright structures, but it has no use of graphic reference means and/or target localizers, it has no biasing means that can effectively stabilize the head movements, it has no repeat positioning to different couches, it is not minimally obstruction-free, it does not use cooperative dental impression, plus biasing means, plus occipital impression means to fix a head or neck position (dental may be substituted here by external contour fixation as shown below), and there are further limitations to the U.K. 2,094,590 invention which the present invention solves.
It is therefore an object of the present invention to provide a head and neck immobilizer, graphic reference means, and/or target localizer that can reposition the patient's head and neck on a couch, and thereafter provide target localization for probe or external irradiation to targets in the head and neck region.
It is further an objective of the present invention to provide a patient immobilizer which is minimally invasive or non-invasive, thus making it convenient and comfortable for a patient who must be placed on a radiation couch repeatedly for fractionated radiation treatments.
Another objective of the present invention is to provide a nearly obstruction-free immobilization device with nonetheless verniated position and angle capability so the patient's head can be oriented conveniently on, for example, a radiation couch and on an imaging couch.
Another objective of the present invention is to provide a patient immobilizer which yields minimal obstruction to radiation beams in solid angles coming from below the skull base or approaching the nasopharynx and neck.
It is an objective of the present invention to give reliable and accurate target localization and head positioning in the mobile region of the nasopharynx and neck for reproducible and precise target positioning and beam delivery in this critical area, especially near the spine and critical organs of the throat to enable high dose delivery to cancerous tumors and minimal dose delivery to critical or radio-sensitive structures nearby.
It is further an objective of the present invention to provide a target localizer and/or graphic reference means which are registered in the same way to the head and nasopharynx so that perturbations of external apparatus, couch, and body movement will minimally affect accurate target localization. The apparatus of the present invention can be used for stereotactic radiosurgery and stereotactic radiotherapy in these regions. It is amenable to use with computer software, computer workstation-based three-dimensional radiation planning, and for target volume and beam delivery. Embodiments of minimally invasive examples of the present invention using registration to the teeth and to the body extremities and/or external contours will be given, and illustration of various biasing means relative to the patient attachment means (dental or contour based) and relative to the over-arm or couch are given.